National Phenology Network's spring leaf index showing the average date that leaves begin to bud across the country...
(KMSP) - We may still have several inches of snow on the ground, but the beginning of our spring bloom isn’t all that far away. While we don’t typically get full leaf coverage for another couple of months, the first signs of spring are already occurring.
The rivers are beginning to melt, the birds are starting to return, and the sun will start setting in the 7 o’clock hour this weekend, all signs that spring is right around the corner. Next up, spring allergies will begin as trees start releasing their pollen well ahead of their leaf arrival.
One way to measure how long we have to go till our spring bloom is with the spring leaf index. The National Phenology Network produces a mathematical model that show our start to spring by taking in climate data from when local plant species begin to bloom under the right conditions. While it’s not a perfect measurement, it gives us a pretty good idea of when and where the spring bloom begins.
According to this model, much of the southern United States is already starting to bloom. While the deep south was roughly a week or two behind schedule for this, the Tennessee and Ohio Valleys, plus the Carolinas, and even DC have already started blooming more than 3 weeks ahead of normal. Similar conditions are found in parts of the Desert Southwest and West Coast.
For Minnesota, leaves typically start budding right around the middle of April, roughly five weeks from now, and then big bloom typically happens in the middle of May. The difference between the first leaf index and first bloom index is that leaf production begins well ahead of what we as humans typically see as the spring bloom. The bloom is the time of year when flowers begin to grow, plants are in full growth mode, and trees are full of leaves.